Combined cycle plant injection water preheating arrangement

ABSTRACT

A combined cycle plant ( 10 ), including a heat recovery steam generator (HRSG) ( 36 ), a working fluid which is heated by the HRSG and effective to operate a steam turbine ( 38 ), and a blowdown heat transfer arrangement ( 90, 92, 94,102, 104 ) configured to capture heat present in blowdown water drawn from the working fluid and to transfer the heat to injection water ( 28 ), a gas turbine engine ( 16 ) having a compressor ( 18 ), a combustor ( 20 ), and a turbine ( 22 ), and a water injection arrangement ( 30 ) configured to inject the injection water into the combustor

FIELD OF THE INVENTION

The invention relates to preheating of injection water used in acombustor of a gas turbine engine that is part of a combined cycle plantby using heat recaptured from blowdown water

BACKGROUND OF THE INVENTION

Combined cycle power plants include a topping cycle to generateelectrical energy and a bottoming cycle to recover and use heat from thetopping cycle. The topping cycle may be a Brayton cycle thatconventionally includes a gas turbine engine The bottoming cycle may bea Rankine cycle that conventionally includes a heat recovery steamgenerator (HRSG) to extract heat energy from the exhaust of the gasturbine engine to heat steam used to power steam turbines that in turngenerate electrical energy

The gas turbine engine combustors may operate on fuel gas or optionallyon fuel oil as a backup. There is typically some drop in performance dueto the use of fuel oil and increased emissions such as oxides ofnitrogen (NOx), which are not desirable. Some combustion arrangementsinclude diluent injection (e g water) which helps reduce NOx emissions.There is a thermodynamic benefit to the Brayton cycle if the injectiondiluent is preheated To accomplish this, low pressure feedwater is takenfrom the bottoming cycle and used as the injection diluent. Since thetopping cycle is more efficient than the bottoming cycle there is a netgain in operating efficiency, thereby justifying the loss to thebottoming cycle

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of thedrawings that show

FIG. 1 is a schematic representation of a combined cycle plant having anexemplary embodiment of a diluent preheating arrangement

FIG. 2 is a schematic representation of a combined cycle plant havinganother exemplary embodiment of a diluent preheating arrangement

FIG. 3 is a schematic representation of a combined cycle plant havinganother exemplary embodiment of a diluent preheating arrangement

FIG. 4 is a schematic representation of a combined cycle plant having avariation of the exemplary embodiment of a diluent preheatingarrangement of FIG. 2.

FIG. 5 is a schematic representation of a combined cycle plant havinganother variation of the exemplary embodiment of a diluent preheatingarrangement of FIG. 2

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have developed a new arrangement for a combinedcycle plant that can be used to preheat injection diluent, such aswater, used in the gas turbine engine combustor This arrangement willmaintain the improved efficiency of the topping cycle but without theassociated decrease in efficiency in the bottoming cycle experiencedunder the conventional arrangement for heating the injection diluent Theresult is a net gain in overall operating efficiency Specifically, theinventors propose to use heat present in blowdown water, such as thatresulting from the operation of any or all of a low pressure (LP) steamdrum, an intermediate pressure (IP) steam drum, a high pressure (HP)steam drum, a low pressure kettle boiler, and an intermediate pressurekettle boiler, any or all of which may be associated with the HRSG ofthe bottoming cycle A typical blowdown flow may be as much as threepercent of the total flow entering the drum or kettle boiler dependingupon water quality. This flow takes its heat energy with it and sincethe blowdown is conventionally exhausted to the atmosphere or down thedrain, the heat energy is lost By extracting this energy that isotherwise wasted, it is no longer necessary to use HRSG feedwater asheated diluent as is conventionally done, and the result is an increasein the efficiency of the bottoming cycle, and hence, of the combinedcycle plant In addition to preheating the diluent, this heat can beapplied to any non-fuel fluid associated with the Brayton cycle,including air and exhaust from the combustion process. Successfulimplementation of this arrangement first requires the combined cycleplant to be operating at base or high part load on oil before the wasteheat can be harvested Utilizing the blowdown mixture is particularlyadvantageous because the blowdown mixture is partially steam and hencecontains relatively high amounts of latent heat that can be recovered asthe steam condenses. Additionally, the steam can be flashed at pressuresabove atmospheric which will result in higher steam pressures andtemperatures available for heat transfer to the fuel.

FIG. 1 is a schematic representation of portions of a combined cycleplant 10 having a topping cycle arrangement 12 and a bottoming cyclearrangement 14. The topping cycle arrangement 12 generates a Braytoncycle via a gas turbine engine 16 that includes a compressor 18, acombustor 20, and a turbine 22 The combustor 20 receives fuel 24 from afuel supply (not shown) and compressed air 26 generated by thecompressor 18 The combustor may operate primarily on fuel gas andsecondarily on fuel oil When operating on fuel oil a diluent 28 may alsobe used The diluent 28 may be injected via a diluent injectionarrangement 30 where it is mixed into the fuel oil and the mixtureinjected into a combustion chamber (not shown) of the combustor 20.Alternately, the fuel oil and diluent 28 may be discretely injected andmix within the combustion chamber.

The fuel 24 and compressed air 26 combust (optionally with the diluent28 added) and generate a flow of combustion products 32 that flows intothe turbine 22 and cause the turbine 22 to rotate. This, in turn, turnsa generator (not shown) which produces electrical energy The combustionproducts 32 expand within the turbine 22 and exit the turbine 22 asexhaust 34 The exhaust 34 still contains valuable heat and much of thisheat is recaptured in the bottoming cycle arrangement 14

The bottoming cycle arrangement 14 generates a Rankine cycle bycapturing the heat from the exhaust 34 and generating steam from thecaptured heat using a heat recovery steam generator (HRSG) 36 The steamis used to turn one or more steam turbines 38 that generate additionalelectrical energy The HRSG 36 defines an exhaust path 42 through whichthe exhaust 34 flows Heat exchangers 44 are distributed in the exhaustpath 42 and are effective to capture the heat present in the exhaust 34and transfer it to a working fluid, such as water For the purpose ofillustration the evaporator sections only are shown, the configurationof superheaters and economizers will vary from plant to plant There maybe multiple stages associated with the bottoming cycle arrangement 14,including any or all of a high pressure (HP) stage 50, an intermediatepressure (IP) stage (52), and a low pressure (LP) stage 54 The HP stage50 includes a HP heat exchanger 60 and an HP drum 62 Likewise, the IPstage 52 includes an IP heat exchanger 70, an IP drum 72, and anoptional IP kettle boiler 74 while the LP stage 54 includes a LP heatexchanger 80, an LP drum 82, and an optional LP kettle boiler 84. Thevarious stages 50, 52, and 54 work together to feed steam to one or moresteam turbines 38

Associated with the HP drum 62, the IP drum 72, and the LP drum 82 arean HP drum blowdown arrangement 90, an IP drum blowdown arrangement 92,and a LP drum blowdown arrangement 94 respectively Likewise, associatedwith the IP kettle boiler 74 and the LP kettle boiler 84 are an IPkettle boiler blowdown arrangement 102 and a LP kettle boiler blowdownarrangement 104 During operation there may be continuous blowdown fromthe drums 62, 72, 82 and the optional kettle boilers 74 and 84 via thesearrangements that is effective to remove contaminants left behind whenwater turns to steam. An HP drum blowdown stream 96 flows from the HPdrum 62. An IP drum blowdown stream 98 flows from the IP drum 72 An LPdrum blowdown stream 100 flows from the LP drum 82. An IP kettle boilerblowdown stream 106 flows from the IP kettle boiler 74 Finally, an LPkettle boiler blowdown stream 108 flows from the LP kettle boiler 84Conventionally, the streams 96, 98, 100, 106, 108 are sent to a blowdowntank 110 where a large amount of heat is lost as steam is vented toatmosphere from the top of the tank Additionally, the blowdown water andits heat which are also present in the tank are either sent down a drainor the heat is lost when this water is recycled into the plant coolingsystem However, the bottoming cycle arrangement 14 disclosed hereinincludes components used to recapture this heat and preheat diluentand/or other non fuel fluids associated with the Brayton cycle.

In the shown exemplary embodiment the HP drum blowdown stream 96 may besent to a blowdown tank 110 which feeds a solitary heat exchanger 112configured to draw heat from the blowdown water and transfer it in theform of steam to the diluent 28 associated with the Brayton cyclearrangement 12 Likewise the IP drum blowdown stream 98 may be sent tothe blowdown tank 110 and the LP drum blowdown stream 100 may also besent to the blowdown tank 110 and ultimately to the solitary heatexchanger 112 where the heat is extracted

In a manner similar to the drum blowdown arrangements, one or all of thekettle boiler blowdown arrangements 102 and 104 may transfer theirrespective streams to the blowdown tank 110 which feeds the solitaryheat exchanger 112. Specifically, the IP kettle boiler blowdown stream106 and the LP kettle boiler blowdown stream 108 would each flow to theblowdown tank 110 and ultimately contribute heat to the diluent 28.

In addition to heating the diluent 28, the blowdown heat could berecovered and transferred to another non fuel fluid associated with theBrayton cycle, including the exhaust 34 from the gas turbine engine 16For example, it is sometimes desirable to maintain a temperature of theexhaust 34 at a cold end 130 of the HRSG 36 above a certain thresholdtemperature This reduces and/or prevents condensation of sulfur out ofthe exhaust 34 and onto the heat exchangers 44 which, in turn, damagesthe heat exchangers 44 In an exemplary arrangement the IP kettle boilerblowdown stream 106 may be routed to an IP kettle boiler blowdownarrangement heat exchanger 140 disposed in the exhaust path 42 andconfigured to transfer heat from the IP blowdown stream 106 to theexhaust 34 nearing the cold end 130 of the HRSG 36. While the IP kettleboiler blowdown is shown heating the exhaust 34 in this exemplaryembodiment, blowdown from any of the drums or kettle boilers may be usedand the blowdown arrangement heat exchanger may be located wherever isdeemed most suitable to effect the proper temperature of the exhaust 34as it approaches the cold end 130 Further, while this exemplaryembodiment of FIG. 1 shows a blowdown heat exchanger for each blowdownarrangement, any number of heat exchangers may be used for each blowdownarrangement, and not all blowdown arrangements need to have a blowdownheat exchanger

FIG. 2 shows a variation of the exemplary embodiment of FIG. 1, wherethe blowdown tank 110 and the solitary heat exchanger 112 are combinedIn such a configuration the solitary heat exchanger 112 may take theform of coils disposed in the blowdown tank 110. The diluent 28 flowsfrom a fuel source (not shown) and optionally fuel 24 flowing from afuel source (not shown) can flow through the coils while the heat fromwithin the blowdown tank 110 heats the diluent 28 and optionally thefuel 24 flowing through the coils Such a consolidation may represent aneconomical manifestation of the disclosures herein.

FIG. 3 is a schematic representation of an alternate exemplaryembodiment of the combined cycle plant 10 having a topping cyclearrangement 12 and a bottoming cycle arrangement 14 In this exemplaryembodiment the HP drum blowdown arrangement 90 may include an HP drumblowdown arrangement heat exchanger 116 configured to draw heat from theHP drum blowdown stream 96 and transfer the heat to the diluent 28 andoptionally to the fuel 24 associated with the Brayton cycle arrangement12. Likewise the IP drum blowdown arrangement 92 includes an IP drumblowdown arrangement heat exchanger 118 configured to draw heat from theIP drum blowdown stream 98 and the LP drum blowdown arrangement 94includes an LP drum blowdown arrangement heat exchanger 120 configuredto draw heat from the LP drum blowdown stream 100

In a manner similar to the drum blowdown arrangements, one or all of thekettle boiler blowdown arrangements 102 and 104 may have an associatedheat exchanger Specifically, the IP kettle boiler blowdown arrangement102 includes an IP kettle boiler blowdown arrangement heat exchanger 122configured to draw heat from the IP kettle boiler blowdown stream 106and the LP kettle boiler blowdown arrangement 104 includes an LP kettleboiler blowdown arrangement heat exchanger 124 configured to draw heatfrom the LP kettle boiler blowdown stream 108 After exiting the blowdownarrangement heat exchangers 116, 118, 120, 122 and 124 the blowdownstreams 96, 98, 100, 106, and 108 would flow to a conventional blowdowntank 136 where any remaining energy would be flashed and the waterrecycled into the plant cooling system

In the exemplary embodiments of FIG. 3 any or all of the blowdown heatexchangers may be employed They may be employed in series as shown Inthis way the diluent 28 is heated using gradually hotter blowdownstreams Alternately, only the drum blowdown arrangements 90, 92, 94could be used and they could be configured serially, or they could beused individually Similarly, only the kettle boiler blowdownarrangements 102 and 104 could be used and they could be configuredserially, or they could be used individually Alternately, anycombination of blowdown heat exchangers in any flow configuration couldbe used

FIG. 4 shows a variation of the exemplary embodiment shown in FIG. 2 Inthis exemplary embodiment, instead of heating the diluent 28 flowingfrom a source (not shown) in the solitary heat exchanger 112, once allthe respective streams are in the blowdown tank 110 live steam itselfcan be extracted from the top of the blowdown tank 110 to become thediluent 28. This gaseous steam embodies the maximum amount of heatingpossible for the diluent 28 The solitary heat exchanger 112 canoptionally be used to heat the fuel 24

FIG. 5 shows another variation of the exemplary embodiment shown in FIG.2. In this exemplary embodiment, instead of heating the diluent 28flowing from a source (not shown) in the solitary heat exchanger 112,heated water could be extracted directly from the blowdown tank 110.This is possible because once all the respective streams are in theblowdown tank 110, the blowdown fluid will exist in the form of livesteam at the top of the blowdown tank 110 and heated liquid water at thebottom of the blowdown tank 110 The heated liquid flow could then bemoved to the diluent injection arrangement 30 by using a small pump 138The pump 138 may be less expensive than a set of coils mounted in theblowdown tank 110

From the foregoing it can be seen that the present inventors haverecognized a previously unrecognized source of energy and developed away to harvest this heat energy Taking the free energy and applying itas proposed herein supplants the prior art need to draw energy from thebottoming cycle This improves the efficiency of the bottoming cyclewhich, in turn, generates an improved overall efficiency of the plant.Consequently, the arrangement disclosed represents an improvement in theart

While various embodiments of the present invention have been shown anddescribed herein, it will be obvious that such embodiments are providedby way of example only Numerous variations, changes and substitutionsmay be made without departing from the invention herein Accordingly, itis intended that the invention be limited only by the spirit and scopeof the appended claims.

The invention claimed is:
 1. A combined cycle plant, comprising a heatrecovery steam generator (HRSG), a working fluid which is heated by theHRSG and effective to operate a steam turbine, and a blowdown heattransfer arrangement configured to capture heat present in blowdownwater drawn from the working fluid and to transfer the heat to injectionwater; a gas turbine engine comprising a compressor, combustor, and aturbine exhausting to the HRSG, and a water injection arrangementconfigured to inject the injection water into the combustor.
 2. Thecombined cycle plant of claim 1, further comprising a steam drum, and ablowdown arrangement configured to remove blowdown from the steam drum,wherein the blowdown heat transfer arrangement is configured to extractheat from the blowdown from the steam drum.
 3. The combined cycle plantof claim 2, wherein the steam drum comprises a first pressure steamdrum, wherein the combined cycle plant further comprises a secondpressure steam drum, and a second blowdown arrangement configured toremove blowdown from the second pressure steam drum, and wherein theblowdown heat transfer arrangement is configured to transfer heat fromblowdown from the first pressure steam drum to the injection water andthen to transfer heat from blowdown from the second pressure steam drumto injection water heated by the heat from the first pressure steam drum4. The combined cycle plant of claim 3, wherein the first pressure steamdrum is an intermediate pressure steam drum and the second pressuresteam drum is a high pressure steam drum
 5. The combined cycle plant ofclaim 1, further comprising a kettle boiler, wherein the blowdown heattransfer arrangement is configured to extract heat from blowdown fromthe kettle boiler
 6. The combined cycle plant of claim 1, wherein theblowdown heat transfer arrangement is further configured to transferheat to a fuel oil used in the combustor.
 7. The combined cycle plant ofclaim 1, wherein the blowdown heat transfer arrangement is furtherconfigured to transfer heat to exhaust from the gas turbine engine thatis flowing though the HRSG.
 8. A combined cycle plant, comprising aBrayton cycle arrangement comprising a compressor, a combustorconfigured to generate a combustion process, and a turbine, a diluentinjection arrangement configured to inject a diluent into the combustionprocess, and a Rankine cycle arrangement configured to receive exhaustfrom the combustion process, and a blowdown heat transfer arrangementconfigured to capture heat produced from a blowdown flow of the Rankinecycle arrangement and to transfer the heat to the diluent.
 9. Thecombined cycle plant of claim 8, wherein the Rankine cycle arrangementcomprises a heat recovery steam generator and an associated steam drum,and wherein the blowdown flow is from the associated steam drum
 10. Thecombined cycle plant of claim 8, wherein the Rankine cycle arrangementcomprises a heat recovery steam generator and a steam drum, wherein theblowdown flow comprises a blowdown flow from the steam drum, and whereinthe blowdown heat transfer arrangement is configured to transfer theheat to the diluent from the blowdown flow from the steam drum
 11. Thecombined cycle plant of claim 8, wherein the Rankine cycle arrangementcomprises a heat recovery steam generator and an associated kettleboiler, and wherein the blowdown flow is from the associated kettleboiler
 12. The combined cycle plant of claim 8, wherein the blowdownheat transfer arrangement is also configured to transfer heat to a fueloil used in the Brayton cycle arrangement.
 13. The combined cycle plantof claim 8, wherein the Rankine cycle arrangement comprises a heatrecovery steam generator configured to receive the exhaust from thecombustion process, and wherein heat is also transferred to the exhaustand is effective to prevent the exhaust from falling below a thresholdtemperature while within the heat recovery steam generator
 14. Acombined cycle plant, comprising a Brayton cycle arrangement; and aRankine cycle arrangement comprising a blowdown arrangement and ablowdown heat transfer arrangement configured to capture heat from theblowdown arrangement and to transfer the heat to a non fuel fluidassociated with the Brayton cycle arrangement
 15. The combined cycleplant of claim 14, wherein the heat is transferred to a diluent injectedinto a combustor of the Brayton cycle arrangement
 16. The combined cycleplant of claim 14, wherein the Rankine cycle arrangement comprises aheat recovery steam generator configured to receive exhaust from a gasturbine engine of the Brayton cycle arrangement, and wherein the heat istransferred to the exhaust and is effective to prevent the exhaust fromfalling below a threshold temperature while within the heat recoverysteam generator
 17. The combined cycle plant of claim 14, wherein theRankine cycle arrangement comprises a heat recovery steam generator andan associated steam drum, and wherein the blowdown arrangement isconfigured to blowdown the associated steam drum.
 18. The combined cycleplant of claim 14, wherein the Rankine cycle arrangement comprises aheat recovery steam generator and an associated kettle boiler, andwherein the blowdown arrangement is configured to blowdown theassociated kettle boiler
 19. The combined cycle plant of claim 14,wherein the blowdown heat transfer arrangement is also configured totransfer heat to a fuel oil used in the Brayton cycle arrangement